This invention generally relates to a device for braking or locking a rotating element, such as brake or clutch, and more particularly, to a device which employs cam-shaped sprags as the locking elements.
Prior clutch or brake devices have used various types of rollers, sprags, or cam elements for engaging and releasing torque transmission between input and output members. Such locking elements have generally taken the form of cylindrical rollers, spherical balls, or cam shapes of various designs. The locking elements in conventional clutch or brake devices have a limit to their torque capacity due to their design and the loading dynamics (two-dimensional in nature). The wear on these conventional locking elements becomes excessive (due to high contact stresses) as the load increases. This reduces the life cycle and performance of the unit and may also result in the elements going xe2x80x9cover-centerxe2x80x9d as the wear progress.
Recent developments have used sprags effectively as the locking elements between the inner and outer races of a clutch or brake. Improvements have also been obtained by using sprags with a three-dimensional shape in the direction of the Z (rotational) axis, in order to provide performance and service life characteristics that are superior to sprags that have only two-dimensional (2D) geometries. An example of a 3D area locking sprag is described in commonly owned U.S. Pat. No. 5,518,094 issued to the same inventor on May 21, 1996, which is incorporated by reference herein for explanation of the general operation of a sprag locking device.
However, it is desirable in the use of 2D or 3D sprags as locking elements to have the ability to quickly and easily disengage or release the sprags of a brake or clutch while they are operating under a holding torque.
In accordance with the present invention, a split locking sprag, adapted to be used as a locking element between an inner race portion and an outer race portion which are moved or driven relative to each other, is comprised of: (a) a pair of sprag subsections mounted opposite each other between the inner and outer races, wherein one sprag subsection has a sprag surface which is engageable with the inner race and the other sprag subsection has a sprag surface which is engageable with the inner race, said sprag subsections being movable relative to each other between a locking position in which the dimensions of the sprag subsections are combined together to present their respective sprag surfaces for engagement with the inner and outer races, and an unlocking position in which the sprag subsections are moved to change their combined dimensions to allow displacement of their respective sprag surfaces out of engagement with the inner and outer races, a biasing element for holding the sprag subsections in the locking position, and an actuator element for applying a release force to move the sprag subsections to the unlocking position.
In a preferred embodiment, a sprag is divided into two or more sections that pivot about a main pivot pin between locked and unlocked positions. A linkage and tripper mechanism allows the sprag sections to be unlocked in a controlled manner by applying a small external force to the tripper. Alternatively, the sprag can be configured in any manner that allows their combined dimensions to be changed when triggered to release a torque while under load. The split locking sprag can be applied to both 2-dimensional and 3-dimensional locking sprag surfaces.
When used as a one way over-running clutch, the sprags can be triggered to instantly release the torque without having to first remove the source of the torque. Since the sprags can be commanded to release independently of the applied torque, they can also be paired in opposite directions so that each sprag pair can hold torque in both directions. In this configuration, the sprag pair acts as a brake. Because traditional sprags cannot be triggered to release (with an applied torque load), they cannot be placed in opposite pairs to act as a brake.